Proximity sensors are used to detect or measure the proximity of a target to the sensor. A known proximity sensor is based on the principle of electric induction, and detects the proximity of a metallic target by monitoring the inductance of a metallic loop of the sensor. However, induction proximity sensors suffer from interference from metallic objects other than the target, and from electromagnetic interference.
Another known proximity sensors is based on the principle of magnetostriction, where the shape or dimension of a magnetostrictive material varies when subjected to varying magnetic field strength. The varying proximity of a magnet to a portion of magnetostrictive material can be determined by measuring a resultant change in shape or dimension of the portion of material. The change in shape or dimension can be interrogated optically, for example via an optical component whose optical characteristics vary in response to a change in shape or dimension.
In some applications, after calibration, a proximity sensor may be used to infer the distance between two objects. For example, a sensor head may be attached to one object, and a target may be attached to a different object. However, a misalignment of either of the sensor head or the target can lead to an erroneous determination of the distance between the objects. For example, if the target is unintentionally shifted in a direction perpendicular to the target-sensor axis, then the sensor will indicate that the distance between the objects is larger than it actually is. Such a shift necessitates recalibration of the sensor-target system and/or access to the target or sensor to realign the sensor and/or target as appropriate. This is time consuming, and in some applications can be problematic due to inaccessibility of the target and/or sensor.